The present invention relates to transmission-receiving techniques and recording-reproduction techniques for signals between apparatuses, or more in particular to an output circuit, a recording apparatus and a reproduction apparatus for digital video signals, in which the digital information signal for moving pictures, programs or the like transmitted by transmission means such as coaxial cable, optical cable, telephone channel or satellite broadcast are received and the received signals are exchanged between apparatuses.
A recording-reproduction apparatus for digital video signals is disclosed, for example, in JP-A-1-258255 (U.S. Pat. No. 5,065,259).
Also, a ITU-T Draft Rec. H.262 standard called MPEG-2 (Moving Picture Experts Group) is known as a scheme for digitally compressing the video signal at high efficiency. On the other hand, a MPEG-2 Systems Working Draft is known as a transmission standard for the video signal and the audio signal compressed by MPEG-2.
The above-mentioned standards present a technique for compressing a program and broadcasting it digitally. The use of this compression scheme with a high compression ratio allows broadcasting of four to eight times more programs than the conventional analog broadcast in the same transmission channel. As a result, a digital satellite service or a similar service called the Near Video On-Demand in which moving pictures of two hours are broadcast repeatedly in 30-minute shifts, for example, has already started in the U.S. Since all programs cannot be broadcast by the Near Video On-Demand service throughout the day, however, there still is a demand for video-recording broadcast signals and viewing programs by playback at convenient times as in the prior art.
A method for recording and reproducing a program which is digitally compressed and digitally broadcast may include decompressing the received digital signal and after converting it into an analog signal, recording it in the conventional analog VTR. The conversion into an analog signal and video-recording by analog VTR spoils the valuable high signal-to-noise ratio of the digital signal.
JP-A-1-258255 discloses a technique for A/D converting an analog video signal input and digitally recording it after bit reduction. In the case of digital braodcasting, however, a high-efficiency digital compression is already employed, and therefore, the decompression and digital recording of the signal as disclosed in the aforementioned JP-A-1-258255 publication fails to obtain a sufficient compression efficiency, or the use of such a high-efficiency digital compressor as used in broadcasting stations for each VTR has a great cost.
It is desired to digitally record the digitally broadcast signal directly. According to the aforementioned MPEG standard, for example, a signal is compressed and the compressed signal is transmitted as packets in a transport stream format. Nevertheless, any technique for recording the digital signal thus transmitted is not yet disclosed.
A digital signal recording apparatus for recording a digitally compressed video signal on the magnetic tape using a rotary head is disclosed in JP-A-5-174496. Measures against recording signals of different transmission rates and signals of different types are not taken into consideration by such an apparatus.
An object of the present invention is to provide an apparatus capable of efficiently recording and reproducing signals compressed according to the MPEG standard, for example, and transmitted.
Another object of the invention is to provide a receiving apparatus and a recording-reproduction apparatus for digital broadcast and a low-cost interfacing circuit.
Still another object of the present invention is to provide an digital signal input-output circuit which can meet any difference in the transmission rate or the format of the recording signal.
According to one aspect of the invention, there is provided a digital video signal input-output circuit for intermittently inputting and outputting a digitally compressed video signal in packet format by a clock signal of a predetermined frequency, wherein the frequency of the clock signal is set to an integer multiple of the rotational speed of the rotary head of the recording-reproduction apparatus, the frame frequency or the field frequency of the video signal.
According to another aspect of the invention, there is provided an output circuit for applying a digital video signal to a data storage apparatus such as a recording medium and intermittently outputting a digitally compressed video signal in packet form including a time stamp, comprising means for detecting a clock reference from a digitally compressed video signal containing the clock reference, means for generating a clock signal in phase with the detected clock reference, means for adding to the packet a time stamp defined as information representing the relative time of transmission of packets according to the clock signal thus generated, and means for outputting a packet of the digitally compressed video signal with a time stamp added thereto.
According to still another aspect of the invention, there is provided an apparatus for recording a digitally compressed video signal containing a clock reference intermittently transmitted in packets having a time stamp as an input signal by means of a rotary head on a magnetic recording medium, comprising means for generating a reference signal for controlling the rotation of the rotary head in phase with the time stamp and means for controlling the rotation of the rotary head on the basis of the rotation control reference signal.
According to a further aspect of the invention, there is provided an apparatus for reproducing a digitally compressed video signal containing a clock reference as an input signal recorded on a magnetic recording medium by a rotary head in phase with the time stamp in a packet, comprising means for reproducing the recorded signal, a local oscillator, temporal adjust means for outputting a packet signal reproduced in accordance with the time stamp contained in the reproduced signal on the basis of the output signal of the local oscillator, a circuit for frequency-dividing the output signal of the local oscillator, and means for controlling the rotation of the rotary head according to the output signal of the frequency-dividing circuit.
In operation, an apparatus having the above-mentioned configuration detects the clock reference contained in the digitally compressed signal and generates a clock signal in phase with the clock reference, thereby producing a clock signal in phase with the digitally compressed signal. A time stamp providing time information generated using this clock signal is added to the signal packet, whereby.a time stamp in synchronization with the digitally compressed signal can be added to the signal packet.
Further, a signal recording operation in synchronization with a digital signal can be effected by generating a rotation control reference signal in phase with the time stamp added to the packet signal and by controlling the rotation of the rotary head in accordance with the reference signal.
Furthermore, in reproducing the signal recorded this way, the reproduced signal is temporally adjusted in accordance with the clock signal generated by a local oscillator, and the time interval of packet signals thus can be securely restored. Also, the rotation of the rotary head is controlled by use of the particular clock signal, whereby any coverage or shortage between a reproduced signal and an output signal is eliminated, thereby realizing a stable reproduction of digital signals.